P89LPC933 datasheet(46/75 Pages) PHILIPS

46 / 75 page

9397 750 15113

Product data sheet

Rev. 06 — 20 June 2005

46 of 75

Philips Semiconductors

P89LPC933/934/935/936

8-bit microcontroller with accelerated two-clock 80C51 core

8.23 Analog comparators

Two analog comparators are provided on the P89LPC933/934/935/936. Input and output

options allow use of the comparators in a number of different conﬁgurations. Comparator

operation is such that the output is a logic 1 (which may be read in a register and/or routed

to a pin) when the positive input (one of two selectable pins) is greater than the negative

input (selectable from a pin or an internal reference voltage). Otherwise the output is a

zero. Each comparator may be conﬁgured to cause an interrupt when the output value

changes.

The overall connections to both comparators are shown in Figure 21. The comparators

function to VDD = 2.4 V.

When each comparator is ﬁrst enabled, the comparator output and interrupt ﬂag are not

guaranteed to be stable for 10 microseconds. The corresponding comparator interrupt

should not be enabled during that time, and the comparator interrupt ﬂag must be cleared

before the interrupt is enabled in order to prevent an immediate interrupt service.

When a comparator is disabled the comparator’s output, COn, goes HIGH. If the

comparator output was LOW and then is disabled, the resulting transition of the

comparator output from a LOW to HIGH state will set the comparator ﬂag, CMFn. This will

cause an interrupt if the comparator interrupt is enabled. The user should therefore

disable the comparator interrupt prior to disabling the comparator. Additionally, the user

should clear the comparator ﬂag, CMFn, after disabling the comparator.

8.23.1 Internal reference voltage

An internal reference voltage generator may supply a default reference when a single

comparator input pin is used. The value of the internal reference voltage, referred to as

VREF, is 1.23 V ± 10 %.

Fig 21. Comparator input and output connections

comparator 1

CP1

CN1

(P0.4) CIN1A

(P0.3) CIN1B

(P0.5) CMPREF

VREF

OE1

change detect

CO1

CMF1

interrupt

002aaa904

CMP1 (P0.6)

change detect

CMF2

comparator 2

OE2

CO2

CMP2 (P0.0)

CP2

CN2

(P0.2) CIN2A

(P0.1) CIN2B

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